1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and to a semiconductor device. More particularly, the present invention relates to the formation of a transistor having a memory cell and to the subsequent formation of an interlayer dielectric film.
2. Description of the Background Art
In order to suppress gate-induced drain leakage (GIDL) caused by concentration of an electric field on a gate edge (which will be described later), sidewalls of a gate interconnection are subjected to thermal oxidation, thereby forming a gate bird""s beak on the gate edge.
A. A conventional method of manufacturing a semiconductor device will be described hereinbelow.
FIGS. 26 through 31 are cross-sectional views for describing a conventional method of manufacturing a semiconductor device.
First, as shown in FIG. 26, a gate oxide film 2 is formed on a substrate 1. Next, a silicon film 3 is formed from; e.g., a phosphorus-doped polysilicon film or a phosphorus-doped amorphous silicon film, on the gate oxide film 2. A silicide film 4 is formed on the silicon film 3. Further, a dielectric film 5 is formed on the silicide film 4.
Next, as shown in FIG. 27, a resist pattern 6a is formed on the dielectric film 5 through the photolithography process.
As shown in FIG. 28 the dielectric film 5 is subjected to dry etching while the resist pattern 6a is taken as a mask, whereby the dielectric film 5 is patterned. Subsequently, the resist pattern 6a is removed.
Next, as shown in FIG. 29, the silicide film 4 and the silicon film 3 are subjected to dry-etching while the thus-patterned dielectric film 5 is taken as a mask. As a result, gate interconnections of desired geometry are formed.
Next, as shown in FIG. 30, source/drain regions 6 are formed in the substrate 1 by means of implanting an impurity into the substrate 1 while the gate interconnections are taken as masks.
Next, as shown in FIG. 31, the substrate 1 is subjected to thermal oxidation, thereby forming a thermal oxide film 17 on the sides of the silicon film 3 and on the sides of the silicide film 4, which the films 3 and 4 together constitute the gate interconnection, as well as on the substrate 1.
Through thermal oxidation, edges (hereinafter called xe2x80x9cgate edgesxe2x80x9d) of each of the gate interconnections are rounded, thereby forming gate bird""s beaks. Accordingly, there can be prevented generation of hot carriers (also called hot electrons), which would otherwise be caused by concentration of an electric field on the gate edges.
Moreover, damage stemming from dry etching or damage resulting from impurity implanting is eliminated through thermal oxidation.
However, the semiconductor device manufactured by the conventional manufacturing method poses the following problems. FIG. 32 is a cross-sectional view for describing a semiconductor device manufactured by the conventional manufacturing method. FIG. 33 is a cross-sectional view for describing that embedding failures have occurred in an interlayer dielectric film of the semiconductor device manufactured by the conventional manufacturing method.
As shown in FIG. 32, silicon (Si) components contained in the silicon film 3 and those contained in the silicide film 4 are subjected to thermal oxidation in the thermal oxidation process, thereby forming the thermal oxide film 17. There arises a first problem of the thermal oxide film 17 receding to the inside of a gate interconnection with reference to the side surfaces of the dielectric film 5. More specifically, the width A of the gate interconnection becomes narrower than that of the gate interconnection formed immediately after etching (i.e., at the time of formation of the gate interconnection), by only the extent to which the thermal oxide film 17 recedes. This results in an increase in the resistance of the gate interconnection, which in turn deteriorates the drive performance of a transistor.
A second problem is that a thermal oxide film 17a formed on the side surfaces of the silicide film 4 becomes thicker than a thermal oxide film 17b formed on the side surfaces of the silicon film 3. In short, both sides of the silicide film 4 assume a bulging shape. This phenomenon is attributable to the silicide film 4 being oxidized to a greater extent than is the silicon film 3.
As shown in FIG. 33, when an interlayer dielectric film 9 is deposited after formation of the thermal oxide film 17, an embedding failure D arises. Even when the substrate 1 is subjected to heat treatment (e.g., a reflow process) in an atmosphere of O2, N2, and H2O after formation of the interlayer dielectric film 9, the embedding failure D is not removed. The embedding failure D extends both toward and away from the viewer of FIG. 33. The embedding failure D brings into conduction a plurality of contacts arranged in the extending direction of the embedding failure D. The thus-manufactured semiconductor device does not operate properly and becomes defective, thereby deteriorating manufacturing yield.
A third problem is that silicon components in the silicide film 4 are reduced with the progress of thermal oxidation and that the silicide film 4 takes up silicon components in the lower silicon film 3 for replenishing depleted silicon components (as indicated by an arrow B shown in FIG. 32). As a result, volume expansion arises in the silicide film 4, and the silicide film 4 spreads into the lower silicon film 3 (as indicated by an arrow C shown in FIG. 32). In this case, stress is exerted up to the gate oxide film 2 located below the silicon film 3, thereby resulting in a decline in the reliability of the gate oxide film 2. Eventually, the reliability of a semiconductor device also deteriorates.
The present invention has been conceived to solve the previously-mentioned problems and a general object of the present invention is to provide a novel and useful method of manufacturing a semiconductor device, and is to a novel and useful semiconductor device.
A more specific object of the present invention is to form gate bird""s beaks without involvement of an increase in the resistance of a gate interconnection and to facilitate embedding of an interlayer dielectric film between gate interconnections.
The above object of the present invention is attained by a following method of manufacturing a semiconductor device and a following semiconductor device.
According to first aspect of the present invention, the method of manufacturing a semiconductor device, comprises the steps of: forming a gate oxide film on a substrate; forming gate interconnections on the gate oxide film, each gate interconnection including a first silicon film and a dielectric film; forming a first diffusion layer by means of implanting an impurity into the substrate while the gate interconnections are taken as a mask; forming a second silicon film over the entire surface of the substrate so as to cover the gate interconnections, after formation of the first diffusion layer; thermally-oxidizing the second silicon film, thereby forming a thermal oxide film; and forming an interlayer dielectric film on the thermal oxide film.
According to second aspect of the present invention, the method of manufacturing a semiconductor device, comprises the steps of: forming a gate oxide film on a substrate; forming gate interconnections on the gate oxide film, each gate interconnection including a first silicon film and a dielectric film; forming a first diffusion layer by means of implanting an impurity into the substrate while the gate interconnections are taken as a mask; forming after formation of the first diffusion layer a second silicon film over the side surfaces of the first silicon film; thermally-oxidizing the second silicon film, thereby forming a thermal oxide film; and forming, after formation of the thermal oxide film, an interlayer dielectric film over the entire surface of the substrate so as to cover the gate interconnections.
According to third aspect of the present invention, the semiconductor device comprises: a substrate; a gate oxide film formed on the substrate; a plurality of gate interconnections which are formed on the gate oxide film, each of the gate interconnections including a first silicon film and a dielectric film; an impurity diffusion layer formed in the substrate between the gate interconnections; a thermal oxide film covering each of the gate electrodes; and an interlayer dielectric film formed on the thermal oxide film; wherein a side surface of the dielectric film and a side surface of the first silicon film constitute a single plane.
Other objects and further feature of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.